Process for manufacturing molded circuit board

ABSTRACT

A molded circuit board is formed by a process comprising the steps of: molding liquid crystal polymer of plating grade into a primary product that has an outline corresponding to the dimensions of said molded circuit board; roughening the surface of said primary product; molding a secondary molded member to produce a secondary product by coating said primary molded member with oxyalkylene-containing poly(vinyl alcohol) resin over almost the entire surface thereof except for a circuit area on which a circuit is to be formed; heating said secondary product; applying catalyst to said circuit area where portions of surface of said primary molded member are not covered with said secondary molded member; heating said secondary product in hot water to elute the secondary molded member into hot water; and chemically plating the catalyst-applied-area to form a circuit thereon. This process minimizes the size of the molded circuit board, simplifies the procedure and thus reduce the production cost.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

[0001] The present invention relates to a process for manufacturing a molded circuit board for an internal antenna or the like by plating a surface only in a limited area thereof such as part of the surface or the inner surface of an aperture provided therein.

[0002] The present inventors previously suggested a process for manufacturing a partially-plated plastic molded product. For manufacturing a circuit substrate, for example, the method comprises the steps of molding a circuit substrate as a primary molded member (primary product) in dies, roughening the surface of the substrate, applying catalyst to the substrate for pre-treatment, placing the pre-treated substrate in dies, coating the substrate with plastic material except for the region of the substrate on which a circuit is to be formed such that the circuit substrate is covered with the plastic but with only the circuit region remaining uncovered (a secondary product), and plating the substrate to produce a final product in which only the circuitry region has been plated.

[0003] In such processes, however, the material that is molded in the second molding step (i.e., secondary molded member) will remain in the final product. To solve this problem, mixture of plastic and filler (e.g., glass fiber) has been used in the second molding step, which resulted in high production cost. Alternatively, resin that requires high-pressure injection has been used though in this case it was difficult to obtain a sufficiently thin and compact circuit since a thicker and wider region may be required for forming a circuit, which makes the substrate thick as a whole.

[0004] Accordingly, one object of the present invention is to provide a process for manufacturing a molded circuit board comprising an additional step of eluting the material molded in the second molding step such that such material will not remain in the final product. Other objects of the invention are to minimize the size of the circuit board, to avoid environmental pollution by using biodegradable resin in the portion which is to be eluted, and to reduce production cost by using material that can be eluted easily and simplifying the procedure.

OBJECT AND SUMMARY OF THE INVENTION

[0005] For the above-described objects, the process for manufacturing a molded circuit board according to the present invention comprises the steps of: injecting liquid crystal polymer of plating grade in a cavity that has an outline corresponding to the dimensions of the molded circuit board to mold a primary product (primary molded member); roughening the surface of the primary product; inserting the primary product into a cavity that forms a gap between the outer surface of said primary product and the inner surface of cavity over almost the entire surface of the member except for the area on which a circuit is to be formed (a circuit area) and then injecting oxylkylene-containing poly(vinyl alcohol) resin into the gap to mold a secondary molded member to produce a secondary product which comprises the primary molded member coated with the secondary molded member; heating said secondary product in a stream of hot air to improve the water resistance thereof; applying catalyst such as palladium and/or gold to said circuit area where part of the surface of said primary molded member is not covered with said secondary molded member; heating said secondary product in hot water to elute the secondary molded material into hot water; and plating the catalyst-applied-area to form a circuit.

[0006] Liquid crystal polymer of plating grade may be used as the material for the primary molded member. This type of polymer has solder-heat-resistance and thus can provide greater resistance against solder reflow when a circuit is formed on the surface of the primary product. Further, the polymer exhibit a unique structure on its surface that is called a “skin layer”, which can provide greater releasability of the primary molded member from the secondary molded member. For the purpose of the present invention, oxyalkylene-containing poly(vinyl alcohol) may desirably be used for forming the secondary molded member due to the following properties: it can be easily melted and molded and thus suitable for injection molding; it is water-soluble and thus can be eluted easily; and it is biodegradable and thus can be reduced to naturally existing materials without polluting environment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIGS. 1A to 1G are cross sectional views of intermediate products formed by the respective steps of the process according to the present invention.

[0008]FIG. 2 is a perspective top view of a molded circuit board produced by the process according to the present invention.

[0009]FIG. 3 is a perspective bottom view of a molded circuit board produced by the process according to the present invention.

[0010]FIG. 4 is an enlarged cross sectional view of the region A defined by the phantom line in FIG. 1E, showing a probable swelling of a secondary member produced by a process similar to the present invention but without heating (annealing) treatment of step 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0011] As one example of the embodiment according to the present invention, a process for manufacturing a molded circuit board 1 as shown in FIGS. 2 and 3 will be described in detail in reference to the steps shown in FIGS. 1A to 1G.

[0012]FIG. 1A shows a primary molded member 10 produced by a first molding step. The primary molded member 10 has an outline feature that corresponds to the dimension of a final product, a molded circuit board 1. Conventional upper and lower dies (not shown) may be used for the first molding step. When engaged with each other, these dies form a cavity defined by their opposing surfaces that corresponds to the step-like outline as shown in FIGS. 2 and 3. In the cavity is provided a pin for forming an aperture 10a through the thicker portion of the molded product. These upper and lower dies are engaged to form a cavity therebetween, and a primary material, liquid crystal polymer of plating grade (polyester resin) is then injected and molded in the cavity.

[0013] The liquid crystal polymer may be any aromatic polyester liquid crystal polymer such as “Vectra” (available from Polyplastics Co., Ltd.) plating grade C810.

[0014] An exemplary conditions for injection molding to be used in the first molding step is given as follows: Injection material “Ventra” plating grade C810 Cylinder temperature 320° C. Die temperature 110° C. Injection pressure 1,200 Kg/cm² Colling time 20 sec.

[0015]FIG. 1B shows a second step of degreasing the primary molded member 10 and roughening (etching) its surface. As a result, all the surfaces of the member 10 have been made rough (course surfaces 10b) including its outer surface and the inner surface of the aperture 10a provided therein. One example of etching involves heating an alkaline solution containing caustic soda or caustic alkali of a predetermined amount (e.g., 45 wt %) dissolved in water to a predetermined temperature such as 50 to 90° c., and soaking the primary molded member 10 in the solution for a predetermined period of time such as 30 minutes. The etching roughens its outer surface entirely (rough surface 10b).

[0016]FIG. 1C shows a secondary product that additionally comprises a secondary molded member 20 molded in the second molding step by using conventional upper and lower dies (not shown). When engaged with each other, they form a cavity defined by their opposing surfaces such that a predetermined gap may be formed between the outer surface of the primary molded member 10 and the inner surfaces of these dies. Protrusions and/or pins are provided on the inner surface of the dies which are positioned so that they oppose to the circuit area and cover in the aperture in such that no gap is formed in the area of the molding circuitry 1 on which the circuitry 4 is to be formed. These dies are combined together to form a cavity therebetween, and a secondary material, oxyalkylene-containing poly(vinyl alcohol) resin is then injected to be molded in the cavity. The secondary molded member 20 released from the dies has a groove 20a on which circuitry is to be formed and a rough surface 10b of the primary molded member 10 uncovered at the bottom surface of the groove or the inner surface of the aperture that communicates to the groove. In other words, the primary molded member 10 is now coated with the secondary molded member 20 except for the area thereof on which a circuitry 3 (see FIG. 1G) is to be formed.

[0017] As an oxyalkylene-containing poly(vinyl alcohol) resin is used, for example, “ECOMATY AX” (available from The Nippon Synthetic Chemical Industry Co., Ltd.).

[0018] One exemplary conditions for the injection molding to be used in the second molding step is given as follows: Injection material “ECOMATY AX” Cylinder temperature 220° C. Die temperature  80° C. Injection pressure 900 Kg/cm² Colling time 30 sec.

[0019] The secondary product obtained is then subjected to heat treatment (annealing) at a fourth step as shown in FIG. 1D. The heat treatment will improve the water resistance of the secondary molded member by using a stream of hot air, particularly atmospheric hot air. Conditions used for the heating step depends on the thickness of the secondary molded member 20. For a secondary molded member of 0.4 mm thick, for example, hot air of 175° c. may be blown into the member for 45 minutes. Hot air of 195° c. will increase the number of double bonds and carbonyl groups present in the poly(vinyl alcohol) to produce hot-water-insolubles. The heat treatment also provides improved crystallinity and water-resistance. Generally, hot air of 130 to 195° c. may be used. Further, it has been proved that air oxygen may cause distinct auto-oxidization and that the material which is insoluble during the early stage of the heat treatment will be converted to soluble by hydrochloric acid treatment.

[0020] The heating step enables formation of the inner surface of the groove 20a in the secondary molded member of the secondary product as shown in FIG. 1E by forming the inner surface vertical to the primary molded member 10 as shown in FIG. 1C, and adding catalyst 3 precisely within a predetermined range, thereby forming a circuit 4 within the predetermined region as shown in FIG. 1E. Without the heating step, however, the second molded member 20 may expand to cover in the groove 20a as shown in FIG. 4. This may prevent the catalyst 3 from being applied precisely to a proper area in the next step. FIG. 4 is an enlarged view of area A defined in FIG. 1E. Phantom line surrounding the catalyst 3 in FIG. 4 shows the predetermined range within which the catalyst should desirably be applied.

[0021]FIG. 1E shows a fifth step of applying catalyst 3 such as palladium and/or gold to the rough surface 10b of the primary molded member 10 that is uncovered at the bottom surface of the groove 20a formed in the secondary molded member 20. Catalyst may be applied by any known method. For example, the secondary product may be soaked in catalyst mixture solution of, for example, tin and palladium, and then activated by acid such as hydrochloric acid or sulfuric acid to deposit palladium on the surface of the secondary product 20. Alternatively, relatively strong reducer such as stannous chloride may be adsorbed on the surface of the product which is then soaked in catalyst solution containing noble metal ions such as gold to deposit the gold on the surface of the product. The product may be soaked in the solution at 15 to 23° c. for 5 minutes.

[0022]FIG. 1F shows a sixth step of heating the catalyst-applied secondary product in hot water to elute the molded portion formed by the second molding step (i.e., the secondary molded member) in the hot water. By soaking the secondary product in hot water at 80° c. for 60 minutes, the “ECOMATY AX” can be eluted in the hot water while “Vectra” plating grade C810, the primary material used in the primary molded member 10 will remain unchanged since the “Vectra” has a heat deformation temperature of 200° c. or more. The product will be then washed with water to obtain a product in which the catalyst 3 has been applied on the predetermined area of the rough surface of the primary molded member 10 (shown in FIG. 1B) on which circuitry is to be formed.

[0023]FIG. 1G shows a seventh step of the process for plating the catalyst-applied-area to form a circuitry 4. Chemical copper plating, chemical nickel plating or the like may be used. Thus, the rough surfaces 10b is plated in the catalyst 3 applied such as a circuit area and the inner rough surface of the apertures 10a, whereby circuit 4 is formed thereon as shown in FIGS. 2 and 3. Finally, moisture is removed from the produce by heating to complete the formation of a conductive circuit to obtain a molded circuit board 1.

[0024] The present invention provides the following advantages:

[0025] It can provide an improved heat resistance as well as an improved releasability of the primary molded member 10 from the secondary molded member 20 since the liquid crystal polymer of plating grade used in the primary molded member has high heat-resistance and can provide a skin layer. It is convenient to use oxyalkylene-containing poly(vinyl alcohol) resin as the secondary material in the secondary molded member 20 since the resin has the following properties: it can be easily melted and molded, thus suitable for injection molding; and it is water-soluble and thus can be eluted easily; it is biodegradable and can be reduced to naturally existing materials without polluting environment. It is possible to minimize the size of the circuit board since the secondary molded portions can be eluted and thus will not remain on the final product. A circuit 4 can be formed precisely within a predetermined range since the heat treatment after the second molding step will enable precise application of the catalyst 3 within a proper range.

[0026] Simple procedure and reduced production cost can be attained since catalyst can be applied only to the area which has not been covered by the secondary molded member (i.e., an uncovered surface on which a circuitry is to be formed), which minimizes the amount of the material required. 

1. A process for manufacturing a molded circuit board, comprising the steps of: molding a primary molded member to produce a primary product that has an outline corresponding to the dimensions of said molded circuit board; roughening the surface of said primary product; molding a secondary molded member to produce a secondary product by coating said primary product with a synthetic resin that has a melting point lower than the heat degradation temperature of said primary molded member over almost its entire surface except for a circuit area on which a circuit board is to be formed; heating said secondary product to improve the water resistance thereof; applying catalyst to said circuit area where portions of surface of said primary molded member are not covered with said secondary molded member; heating said secondary product in hot water to elute the secondary molded member into hot water; and plating the catalyst-applied-area to form a circuit.
 2. The process according to claim 1 wherein said step of molding a primary molded member involves injecting a synthetic resin of plating grade into a cavity that corresponds to said dimensions of said molded circuit board.
 3. The process according to claim 1 wherein said step of molding a secondary molded member involves inserting said primary product having roughened surface into said cavity that forms a gap between the surfaces of said primary product and the cavity over almost its entire surface except for the area on which a circuit is to be formed, and injecting a synthetic resin having a lower melting point than the heat degradation temperature of said primary molded member in said cavity to coat said primary molded member.
 4. The process according to claim 1 wherein said heating step involves heating said secondary product in hot atmospheric air.
 5. The process according to claim 1 wherein said eluting step involves heating said secondary product in hot water to elute the secondary molded member.
 6. The process according to claim 1 wherein said synthetic resin of plating grade used for molding said primary molded member is polyester resin.
 7. The process according to claim 6 wherein said polyester resin is an aromatic polyester liquid crystal polymer.
 8. The process according to claim 1 wherein said synthetic resin that has a melting point lower than the heat degradation temperature of said primary molded member is oxyalkylene-containing poly(vinyl alcohol) resin. 